<!DOCTYPE html>
<html>
    <head>
        <title>document</title>
        <script src="js/vue.js"></script>
    </head>
    <body>
        <div id="app">
            {{num1}}
            <input type="text" v-model.number="num1">
            {{num2}}
            <input type="text" v-model.number="num2">
            {{num1 + num2}}
        </div>
        <script>
            var vm = new Vue({ 
                el: '#app',
                data:{
                    msg: 'hello',
                    num1: 1,
                    num2: 2
                }
            })
        </script>
    </body>
</html>